The technology required to transfer monies between one account to another is referred to as Electronic Funds Transfer (EFT). A device that is used for EFT to facilitate the payment of goods without the requirement of ‘cash’ money to change hands between the buyer and the seller is known as an Electronic Funds Transfer at the Point Of Sale (EFTPOS) device. EFTPOS networks are used around the world.
An EFTPOS device can be summarized as a device that accepts both secure (e.g., customer PINs) and insecure data (e.g., transaction amounts) from a keypad and sends this information to a banking EFTPOS network in a format that informs that network to perform a banking transaction. Secure information is encrypted, and messages are usually authenticated with a Message Authentication Code (MAC) that is the result of a modified encryption of the entire message. These encryption keys exist as part of a hierarchy that allows for the EFTPOS network to change their values throughout the life of the product. The EFTPOS device must ensure the safe keeping of these banking keys at all times.
As only secure data is returned from the keypad in an encrypted form, the EFTPOS device must be configured to prevent the customer from entering any secure information (e.g., PIN) when it is waiting for insecure information to be entered. That is, the EFTPOS device must allow for the customer to discern the difference between secure data entry and insecure data entry. Most usually this is achieved through the use of secure prompts. For example, an EFTPOS device will allow insecure data entry only when the user prompt has been checked by the banking authority to ensure that it contains no ambiguity as to its insecure nature. Therefore, a banking authority would not allow any “secure prompt” that contained an expression similar to ‘Enter PIN’, as this could be used to prompt the customer to enter their PIN when it would not be encrypted.
Thus an EFTPOS device can be said to have the following tasks:                1) The entry of data from a keypad;        2) The prompting of user actions via a display; and        3) The selective encryption of data, using stored banking keys.        
As an EFTPOS device is used to facilitate the transfer of funds between accounts, it is often the target of criminal elements wishing to gain fraudulent access to monies. It is important, then, to understand that the following areas of an EFTPOS device may be open to attack or misuse by such elements:                1) Secure data entered on the keypad may be intercepted prior to encryption;        2) Secure prompts may be altered in an attempt to have the user enter secure data when no encryption is to take place (this alteration could be made to the secure prompt when in-situ of the EFTPOS controller, or en-route to the display); and        3) Banking keys may be extracted from the EFTPOS controller, allowing the attacker to decrypt secure data, and ‘forge’ messages to the bank.        
These attacks are usually prevented by encapsulating the keypad, display and controller within a physically secure casing. The aim of this casing is to detect any attempt to tamper with the device, and render the device inoperable if such an attempt occurs. For this reason EFTPOS devices are usually stand alone devices and used only for the purpose of financial transactions. However, in recent times with the increase of communication technology and communication networks, consideration has been given to enabling EFTPOS transactions to be performed by a person using his or her mobile telephone.
The integration of EFTPOS functionality into personal devices such as mobile phones has hitherto not been accomplished, due mainly to the inability to prevent the attacks outlined above. The physical securing of the casing is too expensive for such a consumer device, and often complicates servicing.
The object of the invention is to provide a display device and a personal device, such as a mobile phone, which enables EFTPOS transactions to be performed with the required degree of security.